Conventionally, inkjet printing has been utilized as superior printing methods applicable to wide variety of recording media and thus vigorous developments have been conducted in terms of recording devices, recording methods, recording materials.
However, inkjet recording apparatuses, having been developed and commercialized heretofore, have to use specific recording media developed for inkjet such as inkjet printing papers or inkjet transparency films or obtaining; (i) good fixation of ink, (ii) so-called “clear” recorded images without blur or bleeding (hereinafter occasionally referred to as “feathering”) around letters or pictures of the images, and (iii) recorded images having high optical density (OD) is difficult. That is, when a recording medium such as paper generally used in offices or homes such as plain paper copier (PPC), letter paper, bond paper, postcard, writing paper, envelope, or report pad, or transparency film (OHP films) commercially available on the market is used, it becomes difficult to simultaneously satisfy the above mentioned (i) to (iii).
Because inkjet printing papers are generally expensive and the inkjet printing papers are coated only on one side thereof, when images are recorded on the other side on which coating has not been conducted, fixation of the image and quality of printed letters significantly decrease. This is one of the reasons why inkjet printing apparatus is not widely used.
Therefore, many trials have been made to obtain; (i) good fixation of ink, (ii) so-called “clear” recorded images without bleeding or feathering around letters or pictures of the images, and (iii) recorded images having high optical density (OD).
For example, following methods have been proposed: (1) using strong alkaline ink having a pH of around 13 (see Patent Literatures 1 to 3), (2) performing recording by heating ink which is solid in room temperature to melt and to be discharged (see Patent Literatures 4 and 5), and (3) performing recording by use of oil-based ink that uses water-insoluble organic solvent as a fluid medium.
Moreover, with regard to the method to obtain good fixation of ink in the above mentioned (i), following methods have been proposed: (4) using ink having a large amount of surface acting agent (see Patent Literature 6), (5) using ink which is a mixture of glycerin, N-methyl-2-pyrrolidon, direct dye, and small amount of surface acting agent having low surface tension, the amount less than the critical micelle concentration (CMC) (see Patent Literature 7), (6) using ink of which pH is strong alkaline and added a fluorine-containing surfactant (see Patent Literatures 1 and 3) and the like.
However, regarding the method (1), since the ink is a strong alkali, there is a risk in handling the ink. Moreover, the ink is fixed well and has a good level of printing on acid paper which uses rosin or the like as size agent, but fixation significantly decreases when used with acid-free paper using alkyl ketene dimer, anhydrous stearic acid or the like, of which production has been recently increasing in Japan. Furthermore, there is a tendency that the quality of printing also is deteriorated a little. In addition, since the strong alkaline ink has a strong osmotic force, the ink may easily penetrate to the opposite side of the paper, causing difficulty in performing printing on the both sides of the paper.
The method (2) is an excellent method which satisfies the above mentioned (i) to (iii) simultaneously. However, it has such problems as the printed part rises and when the printed materials are allowed to accumulate, the printed letters are transferred to other paper or papers stick together. Moreover, as a unit to heat ink is required, the recording apparatus becomes complex.
The method (3) is superior in fixation of ink. However, this method requires measurements to deal with the smell and safety of organic solvent contained in ink. Therefore, this method is used only for industrial purposes, e.g., printing lot number in the bottom of a can, and is not used in an office or home.
The method of using ink described in (4) has a problem in the quality of printing as clarified in Patent Literatures 7 and 8 and therefore is not a good method.
The method of using ink described in (5) has a better fixation of ink compared with the conventional ones. As described in its embodiment, drying rate (hereinafter occasionally referred to as fixation) of the ink is 8 to 15 seconds. However, for the user of the recording apparatus, the 8 to 15 seconds are long and depending on the paper used, if the paper is grabbed by hand immediately after the printing, the hand may get dirty by the ink. Moreover, depending on the type of the paper, feathering occurs noticeably and therefore further improvement is required to this method.
The method of using ink described in (6) allows the time for fixation to be within 5 seconds, but similarly to the above mentioned method of (1), it has problems in its safety, fixation and quality of printing on the acid-free paper, and osmotic force of ink to the opposite side of the paper; therefore, this method is not suitable.
Meanwhile, considering the usage in an office or home and smell, safety, handling easiness of ink, and the like, it is preferable to use water-based ink as the ink for the inkjet. Such water-based ink has a tendency to cause feathering on the part of recoding medium when fingerprint or the like is left thereon. Moreover, depending on the type of paper, quality of printing may significantly differ on the front and backside of the paper. Therefore, when the recording medium is set in an inkjet recording apparatus, due attention must be paid in the handling of the recording medium.
Moreover, for example, in a multi-nozzle type inkjet recording is apparatus using water-based ink including 1 to 5% by mass of water-soluble dye and 20 to 50% by mass of water-soluble organic solvent such as glycol, and having surface tension of almost 40 to 55 mN/m, because of the evaporation of water or the like from nozzles, clogging of a nozzle which does not perform the printing (a nozzle which is not used in printing) may occur in the course of a printing procedure. For example, when “1” is printed after printing “-” continuously for about 120 seconds, the nozzles which were used for the printing of “-” normally discharges ink, but other nozzles do not discharge ink and therefore “1” cannot be printed correctly.
In addition, if the inkjet recording apparatus is left unused after the printing for about, for example, two days, assuming the weekend, ink is often not discharged. This is assumed to be due to increased viscosity of ink caused by evaporation of water from nozzles. This causes a user of the inkjet recording apparatus to perform the operation of solving the no-discharge phenomenon every time the user begins to use the apparatus. Such troubles are relatively more often seen in inkjet recording apparatus that uses relatively less energy to spray the ink, e.g., more often in a foam jet type recording apparatus than an inkjet recording apparatus using a piezo element.
To solve the above mentioned problems, it becomes necessary to incorporate various recovery devices such as a cap, a pump and the like in an inkjet recoding apparatus. This is one of the reasons why the inkjet recording apparatus becomes complex and expensive.
Follow are the problems that papers (recording media) used for inkjet methods currently have:    (1) PPC or other ordinary paper causes blurs and feathering around letters and images and so-called “clear” images cannot be obtained, though the paper has been improved much compared to the conventional one. In addition, image density (optical density: OD) is not sufficient.    (2) Images printed on inkjet paper, or matt coated paper for inkjet, has a relatively high resolution and high image density, but images become matt-like and are not glossy, differently from one printed by an offset printing apparatus.    (3) Glossy inkjet paper enables a user to obtain glossy and high quality image close to silver halide photography when dye-based ink is used, but the price of the medium is so expensive that it is hard to be used in an office or for general industrial purposes.    (4) Coated paper for offset printing is produced much and relatively cheap. However, usability with inkjet has not been considered and therefore the paper has insufficient absorbability of ink and offset blots cause by beading, bleed, or spur, pinholes caused by spur (hereinafter occasionally referred to as “spur mark”) or the like may occur. In addition, the paper has insufficient ink drying property, too.
Therefore, the conventional technology has not yet provided an inkjet recording apparatus that allows its user to obtain (i) so-called “clear” and glossy recorded image without blur, feathering, or bleed around letters or pictures and has excellent printing quality, (ii) recorded images having high optical density (OD), and (iii) image having high uniformity that does not include beading in the solid parts. Also, the apparatus needs to satisfy such characteristics as ink fixation, sharp image, image density, transportability of recording medium, and the like. Such an apparatus has not been proposed yet and further improvement and development of the apparatus is currently demanded.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 56-57862    Patent Literature 2: JP-A No. 57-102970    Patent Literature 3: JP-A No. 57-102971    Patent Literature 4: JP-A No. 61-159470    Patent Literature 5: JP-A No. 62-48774    Patent Literature 6: JP-A No. 55-29546    Patent Literature 7: JP-A No. 56-49771    Patent Literature 8: JP-A No. 55-80477